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norskArtikler, rapporter og annet (matematikk og statistikk): Nye registreringer
Viser treff 81-100 av 328
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Recognition of polar lows in Sentinel-1 SAR images with deep learning
(Journal article; Tidsskriftartikkel, 2022-09-06)In this article, we explore the possibility of detecting polar lows in C-band synthetic aperture radar (SAR) images by means of deep learning. Specifically, we introduce a novel dataset consisting of Sentinel-1 images divided into two classes, representing the presence and absence of a maritime mesocyclone, respectively. The dataset is constructed using the ECMWF reanalysis version 5 (ERA5) dataset ... -
Identifying dietary patterns across age, educational level and physical activity level in a cross-sectional study: the Tromsø Study 2015 - 2016
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-09-15)<p><b>Background</b> A healthy diet can decrease the risk of several lifestyle diseases. From studying the health effects of single foods, research now focuses on examining complete diets and dietary patterns reflecting the combined intake of different foods. The main goals of the current study were to identify dietary patterns and then investigate how these differ in terms of sex, age, educational ... -
Codes from symmetric polynomials
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-10-10)We define and study a class of Reed–Muller type error-correcting codes obtained from elementary symmetric functions in finitely many variables. We determine the code parameters and higher weight spectra in the simplest cases. -
On structure of linear differential operators, acting on line bundles
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-11-14)We study differential invariants of linear differential operators and use them to find conditions for equivalence of differential operators acting on line bundles over smooth manifolds with respect to groups of automorphisms. -
On Multi-Rule and Probability-Dependant Adaptations of Conway’s Game of Life and Their Character
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022)We introduce some novel adaptations of Life-Like Automata. We focus mainly on some modifications of the original rules where the evolution of the system is depending from the step and the zone of the grid. We study also the properties of some novel non-deterministic adaptations. -
Symmetry gaps for higher order ordinary differential equations
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-07-04)The maximal contact symmetry dimensions for scalar ODEs of order ≥ 4 and vector ODEs of order ≥ 3 are well known. Using a Cartan-geometric approach, we determine for these ODEs the next largest realizable (submaximal) symmetry dimension. Moreover, finer curvature-constrained submaximal symmetry dimensions are also classified. -
Data-Driven Robust Control Using Reinforcement Learning
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-02-21)This paper proposes a robust control design method using reinforcement learning for controlling partially-unknown dynamical systems under uncertain conditions. The method extends the optimal reinforcement learning algorithm with a new learning technique based on the robust control theory. By learning from the data, the algorithm proposes actions that guarantee the stability of the closed-loop system ... -
Symmetries of supergeometries related to nonholonomic superdistributions
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-06-06)We extend Tanaka theory to the context of supergeometry and obtain an upper bound on the supersymmetry dimension of geometric structures related to strongly regular bracket-generating distributions on supermanifolds and their structure reductions. -
Greedy weights for matroids
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-12-19)We introduce greedy weights of matroids, inspired by those for linear codes. We show that a Wei duality holds for two of these types of greedy weights for matroids. Moreover we show that in the cases where the matroids involved are associated to linear codes, our definitions coincide with those for codes. Thus our Wei duality is a generalization of that for linear codes given by Schaathun. In ... -
Overview of the MOSAiC expedition: Physical oceanography
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-02-07)Arctic Ocean properties and processes are highly relevant to the regional and global coupled climate system, yet still scarcely observed, especially in winter. Team OCEAN conducted a full year of physical oceanography observations as part of the Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC), a drift with the Arctic sea ice from October 2019 to September 2020. ... -
25 years of self-organized criticality: concepts and controversies
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015-05-28)Introduced by the late Per Bak and his colleagues, self-organized criticality (SOC) has been one of the most stimulating concepts to come out of statistical mechanics and condensed matter theory in the last few decades, and has played a significant role in the development of complexity science. SOC, and more generally fractals and power laws, have attracted much comment, ranging from the very ... -
Classification of simply-transitive Levi non-degenerate hypersurfaces in C^3
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-06-24)Holomorphically homogeneous Cauchy–Riemann (CR) real hypersurfaces <i>M<i/><sup>3</sup>⊂C<sup>2</sup> were classified by Élie Cartan in 1932. In the next dimension, we complete the classification of simply-transitive Levi non-degenerate hypersurfaces <i>M<i/><sup>5</sup>⊂C<sup>3</sup> using a novel Lie algebraic approach independent of any earlier classifications of abstract Lie algebras. Central ... -
Constraining two climate field reconstruction methodologies over the North Atlantic realm using pseudo-proxy experiments
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-07-06)This study presents pseudo-proxy experiments to quantify the reconstruction skill of two climate field reconstruction methodologies for a marine proxy network subject to age uncertainties. The BARCAST methodology (Bayesian Algorithm for Reconstructing Climate Anomalies in Space and Time) is tested for sea surface temperature (SST) reconstruction for the first time over the northern North Atlantic ... -
Symmetry classification of viscid flows on space curves
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-11-01)Symmetries and differential invariants of viscid flows with viscosity depending on temperature on a space curve are given. Their dependence on thermodynamic states of media is studied, and a classification of thermodynamic states is given. -
Continuum mechanics of media with inner structures
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-11-05)We propose a geometrical approach to the mechanics of continuous media equipped with inner structures and give the basic (Navier–Stokes, mass conservation and energy conservation) equations of their motion. -
Exact semidefinite programming bounds for packing problems
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-05-25)In this paper we give an algorithm to round the floating point output of a semidefinite programming solver to a solution over the rationals or a quadratic extension of the rationals. This algorithm does not require the solution to be strictly feasible and works for large problems. We apply this to get sharp bounds for packing problems, and we use these sharp bounds to prove that certain optimal ... -
Lightboard – a new teaching tool at the Faculty of Science and Technology at UiT
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-05-05)We would like to present a new tool that was built by three lecturers at UiT last semester – Lightboard. This tool was used before in other countries and other universities, but never at UiT. The COVID-19 pandemic situation motivated the lecturers to find a way to do online lectures differently. Blackboard and chalk work well for natural sciences as long as the lecture is physical and the teacher ... -
Symmetries and Differential Invariants for Inviscid Flows on a Curve
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-02-04)Symmetries and the corresponding fields of differential invariants of the inviscid flows on a curve are given. Their dependence on thermodynamic states of media is studied, and a classification of thermodynamic states is given. -
Families of Gröbner Degenerations, Grassmannians and Universal Cluster Algebras
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-06-10)Let V be the weighted projective variety defined by a weighted homogeneous ideal J and C a maximal cone in the Gröbner fan of J with m rays. We construct a flat family over A<sup>m</sup> that assembles the Gröbner degenerations of V associated with all faces of C. This is a multi-parameter generalization of the classical one-parameter Gröbner degeneration associated to a weight. We explain how our ... -
Cosheaves
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-10-21)The categories pCS(X,Pro(k)) of precosheaves and CS(X,Pro(k)) of cosheaves on a small Grothendieck site X, with values in the category Pro(k) of prok-modules, are constructed. It is proved that pCS(X,Pro(k)) satisfies the AB4 and AB5* axioms, while CS(X,Pro(k)) satisfies AB3 and AB5*. Homology theories for cosheaves and precosheaves, based on quasi-projective resolutions, are constructed and investigated.
